5.1

• scattering experiment - number of alpha particles scattered by a thin sheet of gold is proportional to the number of neutrons in the nucleus

  • some are clear of all nuclei and pass straight through the gold atoms
  • some are deflected slightly
  • some approach a gold nucleus so closely that it is violently repelled by it and rebound appearing to have had a head on collision
• ions - atoms that have gained or lost electrons, so have a different number of electrons
• proton - a positively charged particle in the nucleus of an atom that has a relative mass of 1836
• neutron - a subatomic particle with a neutral charge and relative mass of 1839
• electron - a negatively charged particle that orbits the nucleus of an atom with relative mass of 1
• proton number Z - number of protons in the nucleus of an atom
• nucleon number A - nuber of protons and neutrons in the nucleus
• isotopes - atoms of the same element with different numbers of neutrons
• hydrogen - one proton

  deuterium - one proton and electron

  tritium - one proton and two neutrons
• $E =$$mc^2$

  c = speed of light

  m = mass

  e = energy of a body
• any reaction in which there is a decrease of mass, called a mass defect, is a source of energy
• nuclear fission - splitting of a large unstable nucleus into two smaller nuclei.
• nuclear reactor - heat from a nuclear reactor produced the steam for the turbines

  moderator - graphite core which slows down the fission neutrons

  heat exchanger - heated gas transfers energy to pipes containing cold water so that the water boils to produce steam

  concrete shield - gives workers protection from gamma emissions and escaping neutrons
• nuclear fusion - the joining of two light nuclei to form a heavier nucleus

  • can only occur if the reacting nuclei have enough to overcome their mutual electrostatic repulsion
  • this can happen if they are raised to a very high temperature so that they collide at very high speeds